The present invention relates to a magnetic tape manufacturing method, particularly to a magnetic tape manufacturing method including a step of smoothing the obverse and reverse surfaces of a magnetic tape.
In a conventional method for manufacturing a magnetic tape, a magnetic liquid is applied to a nonmagnetic carrier of larger width than that of the final tape product to form a magnetic recording layer on the carrier. After the magnetic layer has been subjected to orientation and other required processing, the layer is dried. The surface of the magnetic layer is thereafter smoothed to thereby form a source tape. The source tape is then slivered into prescribed widths of the final magnetic tape.
The smoothing of the surface of the magnetic layer is performed in order to luster the surface, enhance the packing density of the layer, and make uniform the thickness thereof. For this purpose, for example, a pushing force of about 200 to 300 kg/cm may be applied to the carrier and the magnetic layer by a plurality of calendar rolls. The carrier and the magnetic layer may be heated to a temperature of about 60.degree. C. to 100.degree. C. by a heating procedure such as induction heating or hot water heating while the tapes are wound on rolls so that the magnetic layers are softened prior to having their surfaces smoothed. However, since the source tape is slivered after the surface of the magnetic layer on the carrier of the tape has been smoothed, the surface conditions of the magnetic tape cut from the source tape are disturbed at both side edges of the magnetic tape. This can lead to problems such as signal dropout, fluctuations in the audio level of the recorded and reproduced signal, and clinging of magnetic grains dislodged from the magnetic layer to the recording/playback head.
In order to solve this problem, a method has been employed in which surface portions of a magnetic tape slivered from a source tape are smoothed only at and near the side edges of the back coating layer of the tape to thereby increase the strength of the applied film. Such a method has been disclosed in Japanese Unexamined Published Patent Application No. 209727/87. Another conventional method in which a layer is composed of a polishing agent and a lubricant is coated on the side edges of a magnetic tape slivered from a source tape. An example of this method is disclosed in Japanese Unexamined Published Patent Application No. 133320/88. In accordance with yet another conventional method, the side edges of a magnetic tape slivered from a source tape are processed with an organic solvent. Such a method is disclosed in Japanese Patent Application No. 12424/72.
However, in the conventional method disclosed in Japanese Unexamined Published Patent Application No. 209727/87, it is difficult to perform the smoothing of the surface of the magnetic tape because the area to be smoothed is narrow. Moreover, since the surface of the magnetic layer of the source tape is smoothed before the slivering thereof and the surface of the back coating layer of the magnetic tape is smoothed after the slivering of the source tape, the manufacturing efficiency of the magnetic tape is not good.
In each of the other conventional methods disclosed in Japanese Unexamined Published Patent Application No. 133320/88 and Japanese Patent Application No. 12424/72, a plurality of processing steps are required after slivering, and hence the total number of manufacturing steps is high, which increases the cost of manufacturing.